小题大做 – xiao3ti2da4zuo4
Literal meaning of each character = small – problem – big – do/produce
Actually, this is basically the same as the English idiom “make a mountain out of a molehill”. The Chinese version doesn’t use the graphic comparison like we do. They simply say the problem is small but the doing or action is big.
Just in case you don’t know what “make a mountain out of a molehill” means (perhaps you aren’t a native English speaker) this idiom is used to describe when someone is over reacting to a problem. The problem is very small but the person is reacting as if the problem were very big.